Wintermute nailed it. Our sunroom has a vaulted ceiling. There are lots of windows and glass doors. One round window is up above everything else. The sun coming through that window shines on a white wall. I looked out the glass doors and saw that circle reflected in the door, with the deck and backyard in the back ground. I took two pictures through two different doors and then a cloud covered the sun and it disappeared. I thought they were interesting photos. Maybe they explain some other "mysterious" photos of ghosts, flying saucers and stuff.
Howard